Fischer-Tropsch Process In A Radial Reactor

ABSTRACT

In a process for converting synthesis gas to higher hydrocarbons in a tubular reactor, reactants are introduced through an inlet of the reactor. The reactants are passed downwardly through at least one tube to an upper surface of a catalyst carrier where they pass into a passage defined by an inner perforated wall of a catalyst container before passing radially through the catalyst bed towards the perforated outer wall. Reaction occurs as the synthesis gas contacts the catalyst. Unreacted reactant and product is passed out of the container through a perforated outer wall thereof and then upwardly between a skirt and an outer wall of the container, followed by being directed over the end of the skirt and downwardly between the skirt and the reactor tube where heat transfer takes place. These steps are repeated for any subsequent catalyst carrier, then product is removed from an outlet of the reactor.

The present invention relates to a process for the conversion of carbonmonoxide and hydrogen (synthesis gas) to liquid hydrocarbon products inthe presence of a Fischer-Tropsch catalyst.

In the Fischer-Tropsch synthesis reaction a gaseous mixture of carbonmonoxide and hydrogen is reacted in the presence of a catalyst to give ahydrocarbon mixture having a relatively broad molecular weightdistribution. The product is predominantly straight chain, saturatedhydrocarbons which typically have a chain length of more than 2 carbonatoms, for example, more than 5 carbon atoms.

The ability to build hydrocarbons from synthesis gas is an attractivealternative to production of the hydrocarbons by cracking oil. Thisapproach to hydrocarbon make has increased as oil production hasstruggled to keep up with increasing demand for high quality fuel andwill increase further as oil reserves diminish and those reserves becomemore carbon rich.

It is therefore desirable to optimise the Fischer-Tropsch process.Several approaches to this have been made and these have generally beendirected at reactor design or at the catalyst formulation. One of themajor issues with the process is that the heat evolved by the reactionis very substantial being, for example, approximately twice thatproduced by the reaction to produce methanol for the equivalentconversion of carbon oxides.

One approach to handling the high heat evolved is to carry out thereaction in a fixed bed reactor. In this arrangement, catalyst pelletsare loaded inside tubes of an axial reactor. Cooling medium, such asvaporising water, is supplied around the tubes. Reactant gases are thenpassed through the tubes where they contact the catalyst and theFischer-Tropsch reaction takes place. The heat evolved is transferredthrough the tube wall to the surrounding cooling medium. In view of theneed to control the heat within the tube, the size of the tubes islimited to allow the heat to pass readily from the centre of the tubesto the walls where heat exchange occurs. Generally therefore the tubeshave a diameter of less than about 40 mm to ensure the required level ofheat transfer and to prevent the catalyst located towards the centre ofthe tube overheating and thermal runaway occurring. The small size ofthe tubes contributes to the high cost of construction of thesereactors.

Even at the small tube size the catalyst particles have to be relativelysmall in order to ensure reasonable mixing and heat transfer. Inaddition careful selection of conditions such as superficial velocityand gas hourly space velocity has to be made in order to maintain therequired heat transfer and manage the conversion of the reactant gasesat a reasonable overall pressure drop.

For tubes approaching the upper size limit, it has been proposed to uselarger catalyst particle sizes and to incorporate gas and/or liquidrecycles to enhance the tube cooling. However, this approach has somedisadvantages since there is significant resistance to mass transfer inFischer-Tropsch catalyst particles where the reactants and lighterproducts have to travel through wax. This leads to the selectivity tounwanted lighter products increasing and the generation of furtherunwanted heat at the centre of the particle.

In an attempt to address these problems so-called “eggshell” catalystshave been proposed in which the surface of a support is impregnated.However, these catalysts provide less active catalyst per unit volume ofthe reactor and therefore reduce the productivity, and hence economics,of the process.

It has also been proposed to reduce the carbon monoxide to hydrogenratio in the reactant gas to improve the mass transfer of the carbonmonoxide to the centre of the catalyst particle. Whilst this doesimprove the catalyst selectivity, the reaction kinetics are slowed whichcan lead to various problems such as carbide formation which has to beremoved periodically.

A further problem is that reduced catalyst cannot generally be used infixed bed reactors so equipment has to be in place to cater for initialreduction to allow for regeneration of the catalyst if required. In somecases this requires the reactor vessel design conditions to beconsiderably in excess of the normal operating conditions therebyincreasing capital costs.

An alternative approach is to carry out the reaction in a bubble slurryreactor. In this arrangement, small catalyst particles, such as those of150 μm or less, are suspended in the hydrocarbon product and areagitated by the injection of reaction gas at the bottom of the reactor.The gas becomes highly dispersed throughout the reactor and so, intheory, the mass transfer area from gas to catalyst is very large.Additionally, as the catalyst diameter is low, the mass transfer andheat transfer resistances within the catalyst particle are also low.Since the catalyst surface area is relatively large the heat transferfrom catalyst particle to fluid is high so that the particles can bemaintained at approaching fluid temperature conditions. The high heatevolution in the reaction can be managed with internal or external coilsin which water is vaporised. Thus in theory, carrying out the process ina bubble slurry reactor offers various advantages.

However, in practice there can be significant mass transfer resistancesin the bubble slurry reactors such that high water partial pressures canbe experienced inside the catalyst particles. Workers have reportedissues such as catalyst oxidation and catalyst damage due tohydrothermal attack of the catalyst support structures. In addition,catalyst attrition can be a significant problem which can lead toproduct purity and catalyst loss issues caused by the difficulty ofarranging adequate separation of very small particles from the product.

Further cobalt based Fischer-Tropsch catalysts can be susceptible topoisoning by even very low levels of impurities such as sulphur species.This is a particular issue in bubble slurry reactors since, if thesynthesis gas includes poisons, all the catalyst within the reactor willbe exposed to the poison whereas in fixed bed reactors the firstcatalyst to be exposed to the poison tends to act as a guard bed forsubsequent catalyst.

It will therefore be understood that bubble slurry reactors provide achallenging environment for catalysts and therefore long catalyst chargelives are difficult to achieve leading to frequent or continuous removalof spent catalyst and replacement with fresh catalyst charge whichresults in reduced average production per unit of catalyst and increasesthe cost of operating the system.

Further, in order to optimise the operation of the bubble slurryreactor, it has to be relatively tall in order to achieve the requiredlevel of agitation and mass transfer. Sufficient liquid has to becontained in the reactor to accommodate the catalyst at concentrationsin the region of 20 to 30 weight percent which results in a large volumeof contained liquid. When these reactors are operating, the gas hold upswithin the slurry are also significant. This requires extra reactorcapacity to accommodate the slurry bed in the gassed state. Toaccommodate this, the reactors are generally of the order of 60 m inheight. Such large reactors are heavy which makes them expensive anddifficult to deploy. If the plant site is not proximate to a substantialwaterway, the transport issues of such a large reactor become critical.

More recently, it has been suggested that a so-called micro-channelreactor can be used to improve the Fischer-Tropsch reaction system byprocess intensification. Key to this approach is to carry out thereaction in narrow channels between the plates of a steam raisingreactor. In this arrangement high heat transfer coefficients and highspecific productivities can be achieved. This approach also enables masstransfer resistances to be minimised by using highly active catalysts onextended surfaces.

These micro-channel reactors are made by bonding plates to form passagesfor the flow of the cooling medium. These reactors have to be fabricatedby specialists and have to be contained in containment vessels. Thus thecapital costs of these arrangements are substantial. A further problemis that there is a limit to the size at which modular units can bemanufactured and the reactors surprisingly have a high specific weightper unit of production making them costly to manufacture.

As high specific activity is required of the catalysts used inmicro-channel reactors, they tend to operate at higher temperatures andproduce products at the lighter end of the hydrocarbon chain spectrum.

A further problem associated with micro-channel reactors relates to therisk of poisoning, to which as indicated above, Fischer-Tropschcatalysts are particularly susceptible. In a micro-channel reactor therelative amount of catalyst used is low and therefore if poisoningoccurs, a significant reduction in performance will also be observed. Ifthe catalyst becomes deactivated, the developers have stated that it isnecessary to return the reactor module to the factory to have thecatalyst removed and replaced, resulting in high cost and significantdowntime unless costly reactors are maintained as spares. Thusmicro-channel reactors are generally only used in small capacitysituations such as in so-called “flare busting” duties where performanceand costs are less than the problems associated with the disposal ofinconvenient gas.

An alternative arrangement is discussed in WO 2010/069486 in which anumber of adiabatic reactors are arranged in series. Since thetemperature rises described are substantial, this arrangement would notbe expected to deliver good performance with conventionalFischer-Tropsch catalysts. In particular, the high temperatures would beexpected to cause rapid catalyst deactivation. In addition at areasonable overall conversion, a high methane make would be expected.

Thus it will be understood that whilst the various approaches tocarrying out Fischer-Tropsch reactions each offer some advantages, theyalso each have their own disadvantages. There is therefore still a needto provide an improved Fischer-Tropsch process which addresses one ormore of the problems of prior art arrangements.

According to the present invention there is provided a process for theconversion of synthesis gas to higher hydrocarbons by contacting agaseous stream comprising synthesis gas with a particulateFischer-Tropsch catalyst, said process being carried out in a tubularreactor having an inlet and an outlet, said outlet being locateddownstream of the inlet, said reactor comprising one or more tubeshaving located therein one or more carriers for said particulatecatalyst and cooling medium in contact with said at least one tube;

wherein said catalyst carrier comprises:

-   -   an annular container holding catalyst, said container having a        perforated inner wall defining a tube, a perforated outer wall,        a top surface closing the annular container and a bottom surface        closing the annular container;    -   a surface closing the bottom of said tube formed by the inner        wall of the annular container;    -   a skirt extending upwardly from the perforated outer wall of the        annular container from a position at or near the bottom surface        of said container to a position below the location of a seal;        and    -   a seal located at or near the top surface and extending from the        container by a distance which extends beyond an outer surface of        the skirt; said process comprising:    -   (a) introducing the gaseous reactants through the inlet;    -   (b) passing said reactants downwardly through said at least one        tube to the upper surface of the, or the first, catalyst carrier        where they pass into the passage defined by the inner perforated        wall of the container before passing radially through the        catalyst bed towards the perforated outer wall;    -   (c) allowing reaction to occur as the synthesis gas contacts the        catalyst;    -   (d) passing unreacted reactant and product out of the container        though the perforated outer wall and then upwardly between the        inner surface of the skirt and the outer wall of the annular        container until they reach the seal where they are directed over        the end of the skirt and caused to flow downwardly between the        outer surface of the skirt and the inner surface of the reactor        tube where heat transfer takes place;    -   (e) repeating steps (b) to (d) at any subsequent catalyst        carrier; and    -   (f) removing product from the outlet.

The catalyst carrier is described in detail in PCT/GB2010/001931 filedon 19 Oct. 2010 which is incorporated herein by reference.

For the avoidance of doubt, any discussion of orientation, for exampleterms such as upwardly, below, lower, and the like have, for ease ofreference been discussed with regard to the orientation of the catalystcarrier as illustrated in the accompanying drawings. However, where thetubes, and hence the catalyst carrier, are used in an alternativeorientation, the terms should be construed accordingly.

The catalyst container will generally be sized such that it is of asmaller dimension than the internal dimension of the reactor tube intowhich it is placed. The seal is sized such that it interacts with theinner wall of the reactor tube when the catalyst carrier of the presentinvention is in position within the tube. The seal need not be perfectprovided that it is sufficiently effective to cause the majority of theflowing gas to pass through the carrier.

Generally, a plurality of catalyst carriers will be stacked within thereactor tube. In this arrangement, the reactants/products flowdownwardly between the outer surface of the skirt of a first carrier andthe inner surface of the reactor tube until they contact the uppersurface and seal of a second carrier and are directed downwardly intothe tube of the second carrier defined by the perforated inner wall ofits annular container. The flow path described above is then repeated.

The catalyst carrier may be formed of any suitable material. Suchmaterial will generally be selected to withstand the Operatingconditions of the reactor. Generally, the catalyst carrier will befabricated from carbon steel, aluminium, stainless steel, other alloysor any material able to withstand the reaction conditions.

The wall of the annular container can be of any suitable thickness.Suitable thickness will be of the order of about 0.1 mm to about 1.0 mm,preferably of the order of about 0.3 mm to about 0.5 mm.

The size of the perforations in the inner and outer walls of the annularcontainer will be selected such as to allow uniform flow of reactant(s)and product(s) through the catalyst while maintaining the catalystwithin the container. It will therefore be understood that their sizewill depend on the size of the catalyst particles being used. In analternative arrangement the perforations may be sized such that they arelarger but have a filter mesh covering the perforations to ensurecatalyst is maintained within the annular container. This enables largerperforations to be used which will facilitate the free movement ofreactants without a significant loss of pressure.

It will be understood that the perforations may be of any suitableconfiguration. Indeed where a wall is described as perforated all thatis required is that there is means to allow the reactants and productsto pass through the walls. These may be small apertures of anyconfiguration, they may be slots, they may be formed by a wire screen orby any other means of creating a porous or permeable surface.

Although the top surface closing the annular container will generally belocated at the upper edge of the or each wall of the annular container,it may be desirable to locate the top surface below the upper edge suchthat a portion of the upper edge of the outer wall forms a lip.Similarly, the bottom surface may be located at the lower edge of the,or each, wall of the annular container or may be desirable to locate thebottom surface such that it is above the bottom edge of the wall of theannular container such that the wall forms a lip.

The bottom surface of the annulus and the surface closing the bottom ofthe tube may be formed as a single unit or they may be two separatepieces connected together. The two surfaces may be coplanar but in apreferred arrangement, they are in different planes. In one arrangement,the surface closing the bottom of the tube is in a lower plane than thebottom surface of the annular container. This serves to assist in thelocation of one carrier on to a carrier arranged below it when aplurality of containers are to be used. It will be understood that in analternative arrangement, the surface closing the bottom of the tube maybe in a higher plane that the bottom surface of the annular container.

Whilst the bottom surface will generally be solid, it may include one ormore drain holes. Where one or more drain holes are present, they may becovered by a filter mesh. Similarly a drain hole, optionally coveredwith a filter mesh may be present in the surface closing the bottom ofthe tube. Where the carrier is to be used in a non-vertical orientation,the drain hole, where present will be located in an alternative positioni.e. one that is the lowest point in the carrier when in use.

One or more spacer means may extend downwardly from the bottom surfaceof the annular container. The, or each, spacer means may be formed asseparate components or they may be formed by depressions in the bottomsurface. Where these spacer means are present they assist in providing aclear path for the reactants and products flowing between the bottomsurface of the first carrier and the top surface of a second lowercarrier in use. The spacer may be of the order of about 4 mm to about 15mm, or about 6 mm, deep. Alternatively, or additionally, spacer meansmay be present on the top surface.

The top surface closing the annular container may include on its uppersurface means to locate the container against a catalyst carrier stackedabove the container in use The means to locate the container may be ofany suitable arrangement. In one arrangement it comprises an upstandingcollar having apertures or spaces therein to allow for the ingress ofreactants.

The upwardly extending skirt may be smooth or it may be shaped. Anysuitable shape may be used. Suitable shapes include pleats,corrugations, and the like. The pleats, corrugations and the like willgenerally be arranged longitudinally along the length of the carrier.The shaping of the upstanding skirt increases the surface area of theskirt and assists with the insertion of the catalyst carrier into thereaction tube since it will allow any surface roughness on the innersurface of the reactor tube or differences in tolerances in tubes to beaccommodated.

Where the upwardly extending skirt is shaped, it will generally beflattened to a smooth configuration towards the point at which it isconnected to the annular container to allow a gas seal to be formed withthe annular container. The upstanding skirt will generally be connectedto the outer wall of the annular container at or near the base thereof.Where the skirt is connected at a point above the bottom of the wall,the wall will be free of perforations in the area below the point ofconnection. The upstanding skirt may be flexible.

Generally, the upstanding skirt will stop at about 0.5 cm to about 1.5cm, preferably about 1 cm, short of the top surface of the annularcontainer.

Without wishing to be bound by any theory, it is believed that theupstanding skirt serves to gather the reactants/products from theperforated outer wall of the annular container and direct them via theshapes towards the top of the catalyst carrier collecting morereactants/products exiting from the outer wall of the annular containeras they move upwardly. As described above, reactants/products are thendirected down between the tube wall and the outside of the upstandingskirt. By this method the heat transfer is enhanced down the wholelength of the carrier but as the heat exchange is separated from thecatalyst, hotter or colder as appropriate heat exchange fluid can beused without quenching the reaction at the tube wall and at the sametime ensuring that the temperature of the catalyst towards the centre ofthe carrier is appropriately maintained.

The seal may be formed in any suitable manner. However, it willgenerally be sufficiently compressible to accommodate the smallestdiameter of the reactor tube. The seal will generally be a flexible,sliding seal. In one arrangement, an O-ring may be used. A compressiblesplit ring or a ring having a high coefficient of expansion could beused. The seal may be formed of any suitable material provided that itcan withstand the reaction conditions. In one arrangement, it may be adeformable flange extending from the carrier. The flange may be sized tobe larger than the internal diameter of the tube such that as thecontainer is inserted into the tube it is deformed to fit inside andinteract with the tube.

In the present invention, the annular space between the outer surface ofthe catalyst container and the inner surface of the tube wall is small,generally of the order of from about 3 mm to about 10 mm. This narrowgap allows a heat transfer coefficient to be achieved such that anacceptable temperature difference of the order of about 10° C. to about40° C. between the cooled exit gas and the coolant to be achieved.

The size of the annulus between the skirt and the catalyst wall and theskirt and the tube wall will generally be selected to accommodate thegas flow rate required while maintaining high heat transfer and lowpressure drop. Thus the process of the present invention may additionalinclude the step of selecting the appropriate size of the annulus tomeet these criteria.

The process of the present invention enables relatively large reactortubes to be used. In particular, tubes having diameters in the region offrom about 75 mm to about 130 mm or even about 150 mm can be usedcompared to diameters of less than about 40 nun used in conventionalsystems. The larger diameter tubes will allow capacity in the region of10,000 US bbl/day to be achieved in a single reactor of less than 6 m indiameter and less than 700 tonnes in weight.

As discussed above the highly exothermic nature of the Fischer-Tropschreaction is a major factor in the design of a reactor in which thereaction can be carried out. The use of the catalyst carrier in theprocess of the present invention, allows tubes comprising a plurality ofcatalyst carriers to become, in effect, a plurality of adiabaticreactors with inter-cooling.

Any suitable catalyst may be used in the process of the presentinvention. Powdered, foamed, structured, or other suitable forms may beused.

One benefit of the process of the present invention is that the carrierallows for the deployment of small diameter Fischer-Tropsch catalysts tobe used such as those having diameters of from about 100 μm to about 1mm. Since these are used in a fixed bed, the mass transfer resistancescan be greatly reduced over prior art arrangements. This will lead toimproved selectivity to the required products, particularly those havinga carbon chain length of five and above.

Further, as these small catalysts have a high surface area and arelocated in the direct flow of the reacting gas, they are maintained at atemperature which is very similar to that of the flowing gas. This willreduce the tendency to by-product formation.

In one alternative arrangement, a monolith catalyst may be used. In thisarrangement, the structure of the catalyst container may be modified.Full details of a catalyst container suitable for use with a monolithcatalyst is described in GB patent application no 1105691.8 filed 4 Apr.2011 the contents of which are incorporated herein by reference.

Thus according to a second aspect of the present invention there isprovided a process for the conversion of synthesis gas to higherhydrocarbons by contacting a gaseous stream comprising synthesis gaswith a monolith Fischer-Tropsch catalyst, said process being carried outin a tubular reactor having an inlet and an outlet, said outlet beinglocated downstream of the inlet, said reactor comprising one or moretubes having located therein one or more carriers for said monolithcatalyst and cooling medium in contact with said tubes; wherein saidcatalyst carrier comprises:

-   -   a container holding a monolith catalyst, said container having a        bottom surface closing the container and a skirt extending        upwardly from the bottom surface of said container to a position        below the location of a seal and spaced therefrom, said skirt        being positioned such that there a space between an outer        surface of the monolith catalyst and the skirt; and    -   a seal located at or near a top surface of the monolith catalyst        and extending from the monolith catalyst by a distance which        extends beyond an outer surface of the skirt; said process        comprising:    -   (a) introducing the gaseous reactants through the inlet;    -   (b) passing said reactants downwardly through said at least one        tube to the upper surface of the, or the first, monolith        catalyst where they pass through the monolith catalyst;    -   (c) allowing reaction to occur as the synthesis gas contacts the        catalyst;    -   (d) passing unreacted reactant and product out of the catalyst        and then upwardly between the inner surface of the skirt and the        outer surface of the monolith catalyst until they reach the seal        where they are directed over the end of the skirt and caused to        flow downwardly between the outer surface of the skirt and the        inner surface of the reactor tube where heat transfer takes        place;    -   (e) repeating steps (b) to (d) at any subsequent catalyst        carrier; and    -   (f) removing product from the outlet.

In one arrangement, the monolith catalyst is a solid, in that there issubstantially no space within the body of the monolith that is notoccupied by catalyst. When the monolith is in use in a vertical reactorwith downflow, the reactant(s) flow downwardly through the reactor tube,the reactant(s) first contacts the upper face of the monolith catalystand flows therethrough in a direction parallel to the axis of thecylinder. The seal of the container prevents the reactant(s) fromflowing around the monolith and assists the direction of the reactantsinto the catalyst. Reaction will then occur within the monolithcatalyst. The product will then also flow down through the monolith in adirection parallel to the axis of the cylinder.

Once the reactant(s) and product reach the bottom surface of thecatalyst carrier they are directed towards the skirt of the carrier. Tofacilitate this flow, feet may be provided within the carrier on theupper face of the bottom surface such that, in use, the catalystmonolith is supported on the feet and there is a gap between the bottomof the catalyst monolith and the bottom surface of the catalyst carrier.The upwardly extending skirt then directs the reactant(s) and productupwardly between the inner surface of the skirt and the outer surface ofthe monolith catalyst until they reach the underside of the seal. Theyare then directed, by the underside of the seal, over the end of theskirt and they then flow downwardly between the outer surface of theskirt and the inner surface of the reactor tube where heat transfertakes place.

In one alternative arrangement, the monolith catalyst has a channelextending longitudinally therethrough. Generally the channel will belocated on the central axis of the monolith catalyst. Thus where thereactor tube is of circular cross-section, the monolith catalyst of thisarrangement will be of annular cross-section. In this arrangement, inuse, in a vertical reactor with downflow, reactant(s) flow downwardlythrough the reactor tube and thus first contacts the upper surface ofthe monolith catalyst. The seal blocks the passage of the reactant(s)around the side of the catalyst. Since the path of flow of reactant(s)is impeded by the catalyst, it will generally take the easier path andenter the channel in the monolith. The reactant(s) then enters theannular monolith catalyst and passes radially through the catalysttowards the outer surface of the catalyst monolith. During the passagethrough the catalyst monolith reaction occurs. Unreacted reactant andproduct then flow out of the monolith catalyst though the outer surfacethereof. The upwardly extending skirt then directs reactant and productupwardly between the inner surface of the skirt and the outer wall ofthe monolith catalyst until they reach the seal. They are then directed,by the underside of the seal, over the end of the skirt and flowdownwardly between the outer surface of the skirt and the inner surfaceof the reactor tube where heat transfer takes place.

In the arrangement in which the monolith catalyst includes the channel,the catalyst carrier may include a top surface which will extend overthe monolith catalyst but leave the channel uncovered. This top surfaceserves to ensure that the reactant(s) do not enter the catalyst monolithfrom the top but are directed into the channel for radial flow.

The discussion of the specific features of the catalyst carrier above inrelation to the first embodiment applies equally in connection to thecatalyst carrier for a monolith catalyst of the second embodimentinsofar as the relevant features are present.

Whichever type of carrier is used, in one arrangement more than 40carriers, preferably more than 41 carriers are located within a singletube. More preferably, from about 70 to about 200 carriers may be used.This will enable a reasonable temperature rise of the order of fromabout 10° C. to about 20° C. to be maintained over each stage.

The radial flow through the, or each, catalyst carrier within the tubemeans that the gas flow path length is also very low when compared withprior art arrangements. Total catalyst depths of the order of about 2metres may be achieved within a tube of up to 20 metres of length atcatalyst hourly space velocities of about 4000. The low flow path meansthat the overall pressure drop achieved is an order of magnitude lowerthan that which would be experienced with the same catalyst in an axialtube not using the process of the present invention.

One advantage of being able to achieve a low overall pressure drop bythe process of the present invention is that long tubes with highsuperficial gas velocities, gases containing high quantities of inertsor a gas recycle may be accommodated without the pressure drop andpotential for catalyst crushing disadvantages experienced with highflows through current fixed bed systems. The ability to accommodaterecycle will enable overall conversion at lower per pass conversions tobe achieved at high catalyst productivity and selectivity.

The reduced catalyst may be repeatedly and reliably reduced and loadedinto the carrier at a manufacturing facility and the balance of thecontainer can be filled with wax. The containers may be assembled inconnected units which will simplify the loading of the reactor and inparticular will mean that the operators do not have to come into contactwith the catalyst. The unloading procedure is also simplified since thecarriers may be readily discharged before being taken for reprocessing.

In one arrangement of the present invention, a plurality of reactors maybe used in parallel.

Liquid product stream separated from the stream exiting the reactor willbe recovered. In the process of the present invention, unreacted gasexiting the outlet of the, or each, reactor may be further treated toremove heat. The removed heat may be reused and/or rejected to cooling.Liquid product separated from the stream exiting the reactor will berecovered.

In one arrangement, two or more reactors may be located in series fluidcommunication with facilities located between each reactor to removeheat. The heat may be reused and/or rejected to cooling. In onearrangement, hydrogen and carbon monoxide containing steam exiting thelast stage of a series of interconnected reactors may be recycled to anysuitable point in the process. In one arrangement it will be recycled tothe inlet of the first reactor.

In one alternative arrangement, two or more groups of parallel reactorsmay be located in series. In this arrangement, groups of parallelreactors are in series communication with facilities located betweeneach group to remove heat. The heat may be reused and/or rejected tocooling. In one arrangement, liquid product may be removed between eachstage with hydrogen and carbon monoxide containing steam being passed toa subsequent reactor group in the series. Hydrogen and carbon monoxidecontaining steam exiting the last stage of a series of interconnectedreactors may be recycled to any suitable point in the process. In onearrangement it will be recycled to the inlet of the first reactor.

Where the process includes a plurality of reaction stages, a hydrogenrich stream may be fed to the second and/or one or more of anysubsequent stages.

Any suitable reaction conditions may be used. In one arrangement, thereaction temperature will be from about 190° C. to about 250° C. Thereaction pressure may be from about 20 bara to about 80 bara.

The present invention will now be described, by way of example, byreference to the accompanying drawings in which:

FIG. 1 is a perspective view from above of the catalyst carrier of thepresent invention;

FIG. 2 is a perspective view of the catalyst carrier from below;

FIG. 3 is a partial cross section viewed from the side;

FIG. 4 is a simplified diagram of the catalyst carrier of the presentinvention;

FIG. 5 is a schematic illustration of a carrier of the present inventionfrom below when located within a tube;

FIG. 6 is a schematic cross section of three catalyst carriers locatedwithin a tube;

FIG. 7 is an enlarged cross-section of Section A of FIG. 6;

FIG. 8 is a schematic representation of an alternative embodiment of thepresent invention, illustrating the flow path;

FIG. 9 is a schematic representation of a third embodiment of thepresent invention, illustrating the flow path; and

FIG. 10 is a schematic representation of the flow path between twostacked carriers of the kind illustrated in FIG. 9.

A catalyst carrier 1 of the present invention is illustrated in FIGS. 1to 3. The carrier comprises an annular container 2 which has perforatedwalls 3, 4. The inner perforated wall 3 defines a tube 5. A top surface6 is closes the annular container at the top. It is located at a pointtowards the top of the walls 3, 4 of the annular container 2 such that alip 6 is formed. A bottom surface 7 closes the bottom of the annularcontainer 2 and a surface 8 closes the bottom of tube 5. The surface 8is located in a lower plane that that of the bottom surface 7. Spacermeans in the form of a plurality of depressions 9 are located present onthe bottom surface 7 of the annular container 2. Drain holes 10, 11 arelocated on the bottom surface 7 and the surface 8.

A seal 12 extends from the upper surface 6 and an upstanding collar 13is provided coaxial with the tube 5.

A corrugated upstanding skirt 14 surrounds the container 2. Thecorrugations are flattened in the region L towards the base of thecarrier 1.

A catalyst carrier 1 of the present invention located in a reactor tube15. The flow of gas is illustrated schematically in FIG. 4 by thearrows.

When a plurality of catalyst carriers of the present invention arelocated within a reactor tube 15 they interlock as illustrated in FIGS.6 and 7. The effect on the flow path is illustrated in the enlargedsection shown in FIG. 7.

A catalyst carrier 101 of a second embodiment is illustrated in FIG. 8.A bottom surface 102 closes the bottom of the container 101. Feet 103extend upwardly from the bottom surface to support a monolith catalyst104. An upstanding skirt 105 extends from the bottom surface 102. Theskirt may be corrugated and may be flattened as in a region towards thebottom surface 103.

A seal 106 is provided to extend from the monolith catalyst 104 andinteract with the wall of the reactor tube 107. Baffles 108 extendupwardly for the seal. These serve to direct flow and to separate thecarrier from the bottom surface of a carrier located above the carrier.The flow of gas is illustrated schematically by the arrows.

An alternative embodiment of the present invention is illustrated inFIG. 9. In this arrangement the monolith catalyst 104 has a longitudinalchannel 109 therethrough. In this arrangement, the feet of the firstembodiment may be omitted. This carrier is similar in arrangement to thefirst embodiment. However, additionally a top surface 110 is provided tocover the upper surface of the monolith catalyst. The flow of gas in thearrangement of FIG. 9 is illustrated schematically by the arrows.

When a plurality of catalyst carriers of the present invention arelocated within a reactor tube 107 the effect on the flow path isillustrated in the enlarged section shown in FIG. 10.

It will be understood that whilst the catalyst carriers have beendescribed with particular reference to a use in a tube of circularcross-section the tube may be of non-circular cross-section for example,it may be a plate reactor. Where the tube is of non-circularcross-section, the carrier will be of the appropriate shape. In thisarrangement, in the the embodiment described in which an annularmonolith is used it will be understood that the monolith will not be acircular ring and this term should be construed accordingly.

The present invention will now be discussed with reference to thefollowing example:

EXAMPLE 1

Conventional fixed bed reactors, currently in production are capable ofproducing approximately 5833 US barrels/day of Fischer-Tropsch liquids.Public disclosures indicate that these reactors weight 1200 tonnes andhave a diameter of 7.2 m and contain over 28000 tubes. A reactor for theprocess of the present invention processing feed gas containing hydrogenand carbon monoxide derived from natural gas with a diameter of 5.6 mwill produce around 10000 US barrels/day of Fischer-Tropsch liquids andwill contain approximately 2300 axial tubes each filled with about 80catalyst carriers and will weigh approximately 700 tonnes. It willtherefore be understood that this represents an improvement of almost afactor of three in the specific weight installed per unit of productionover the prior art arrangements.

1. A process for the conversion of synthesis gas to higher hydrocarbonsby contacting a gaseous stream comprising synthesis gas with aparticulate Fischer Tropsch catalyst, said process being carried out ina tubular reactor having an inlet and an outlet, said outlet beinglocated downstream of the inlet, said reactor comprising one or moretubes having located therein one or more carriers for said particulatecatalyst and cooling medium in contact with said tubes; wherein saidcatalyst carrier comprises: an annular container for holding catalyst inuse, said container having a perforated inner wall defining a tube, aperforated outer wall, a top surface closing the annular container and abottom surface closing the annular container; a surface closing thebottom of said tube formed by the inner wall of the annular container; askirt extending upwardly from the perforated outer wall of the annularcontainer from a position at or near the bottom surface of saidcontainer to a position below the location of a seal; and a seal locatedat or near the top surface and extending from the container by adistance which extends beyond an outer surface of the skirt; saidprocess comprising: (a) introducing the gaseous reactants through theinlet; (b) passing said reactants downwardly through said at least onetube to the upper surface of the, or the first catalyst carrier wherethey pass into the passage defined by the inner perforated wall of thecontainer before passing radially through the catalyst bed towards theperforated outer wall; (c) allowing reaction to occur as the synthesisgas contacts the catalyst; (d) passing unreacted reactant and productout of the container though the perforated outer wall and then upwardlybetween the inner surface of the skirt and the outer wall of the annularcontainer until they reach the seal where they are directed over the endof the skirt and caused to flow downwardly between the outer surface ofthe skirt and the inner surface of the reactor tube where heat transfertakes place; (e) repeating steps (b) to (d) at any subsequent catalystcarrier; and (f) removing product from the outlet.
 2. The processaccording to claim 1 wherein the catalyst particles have a diameter offrom about 100 mm to about 1 mm.
 3. A process for the conversion ofsynthesis gas to higher hydrocarbons by contacting a gaseous streamcomprising synthesis gas with a monolith Fischer Tropsch catalyst, saidprocess being carried out in a tubular reactor having an inlet and anoutlet, said outlet being located downstream of the inlet, said reactorcomprising one or more tubes having located therein one or more carriersfor said monolith catalyst and cooling medium in contact with saidtubes; wherein said catalyst carrier comprises: a container holding amonolith catalyst, said container having a bottom surface closing thecontainer and a skirt extending upwardly from the bottom surface of saidcontainer to a position below the location of a seal and spacedtherefrom, said skirt being positioned such that there is a spacebetween an outer surface of the monolith catalyst and the skirt; and aseal located at or near a top surface of the monolith catalyst andextending from the monolith catalyst by a distance which extends beyondan outer surface of the skirt; said process comprising: (a) introducingthe gaseous reactants through the inlet; (b) passing said reactantsdownwardly through said at least one tube to the upper surface of the,or the first, monolith catalyst where they pass through the monolithcatalyst; (c) allowing reaction to occur as the synthesis gas contactsthe catalyst; (d) passing unreacted reactant and product out of thecatalyst and then upwardly between the inner surface of the skirt andthe outer surface of the monolith catalyst until they reach the sealwhere they are directed over the end of the skirt and caused to flowdownwardly between the outer surface of the skirt and the inner surfaceof the reactor tube where heat transfer takes place; (e) repeating steps(b) to (d) at any subsequent catalyst carrier; and (f) removing productfrom the outlet.
 4. The process according to claim 1 wherein a pluralityof catalyst carriers are stacked within the reactor tube.
 5. The processaccording to claim 1 wherein the annular space between the outer surfaceof the catalyst container and the inner surface of the tube wall isselected to accommodate the gas flow rate required while maintaininghigh heat transfer and low pressure drop.
 6. The process according toclaim 1 wherein the annular space between the outer surface of thecatalyst container and the inner surface of the tube wall is of theorder of from about 3 mm to about 10 mm.
 7. The process according toclaim 1 wherein the one or more tubes have a diameter of from about 75mm to about 150 mm.
 8. The process according to claim 1 wherein morethan 41 carriers are located within a single tube.
 9. The processaccording to claim 1 wherein from about 70 to about 200 carriers arelocated within a single tube.
 10. The process according to claim 1wherein a plurality of reactors are used in parallel.
 11. The processaccording to claim 1 wherein unreacted gas exiting the outlet of theeach or each reactor is treated to remove heat.
 12. The processaccording to claim 11 wherein the removed unreacted gas is reused. 13.The process according to claim 1 wherein two or more reactors arelocated in series.
 14. The process according to claim 13 wherein thereactors located in series are in fluid communication with facilitieslocated between each reactor to remove heat.
 15. The process accordingto claim 13 wherein hydrogen and carbon monoxide containing steamexiting the last stage of the series of interconnected reactors isrecycled to any suitable point in the process.
 16. The process accordingto claim 15 wherein hydrogen and carbon monoxide containing steamexiting the last stage of the series of interconnected reactors isrecycled to the first reactor.
 17. The process according to claim 9wherein groups of parallel reactors are in series communication withfacilities located between each group to remove heat.
 18. The processaccording to claim 13 wherein the heat is reused and/or rejected tocooling.
 19. The process according to claim 17, wherein liquid productis removed between each group of parallel reactors with hydrogen andcarbon monoxide containing steam being passed to a subsequent reactiongroup in the series.
 20. The process according to claim 19 whereinhydrogen and carbon monoxide containing steam exiting the last stage ofa series of interconnected reactors is recycled to any suitable point inthe process.
 21. The process according to claim 20 wherein the stream isrecycled to the inlet of the first reactor.
 22. The process according toclaim 9 wherein a hydrogen rich stream is fed to the second and/or oneor more of any subsequent reactors or subsequent reactors.
 23. Theprocess according to claim 1 wherein the reaction temperature is fromabout 190° C. to about 250° C.
 24. The process according to claim 1wherein the reaction pressure is from about 20 bara to about 80 bara.